Device for surgery of the cornea

ABSTRACT

A device for surgery of the cornea includes an annular base for fixing the device to the eye of a patient and a cutter head including a body and a blade assemble. The blade assembly includes a blade and a blade carrier with a resilient tongue integral with the blade carrier. The resilient tongue has a stud located at one end. The cutter head is a one piece body with provisions to connect it to a drive. An orifice is formed in the body for accepting the blade assembly.

This application is a divisional of application Ser. No. 09/974,816,filed on Oct. 12, 2001, now U.S. Pat. No. 6,647,594 the entire contentsof which are hereby incorporated by reference and for which priority isclaimed under 35 U.S.C. § 120; and this application claims priority ofApplication No. 0013067 filed in France on Oct. 12, 2000 under 35 U.S.C.§ 119.

The present invention relates to a device for surgery of the cornea, inparticular a keratome capable of slicing a sliver from the cornea,either to separate it completely or to leave it as a flap.

BACKGROUND OF THE INVENTION

There exist numerous apparatuses suitable for implementing thisoperation (resection of the cornea). The technique of sliver resectionbegan to be implemented more than 50 years ago and apparatuses have beenunder development ever since. This development has been directedessentially at two points: the means for cutting the corneal disk andthe means for advancing the cornea-cutting means.

Two main types of cutter means are to be found at present: blades withcircular motion (such as Prof. Draeger's microkeratome, for example) andblades with alternating rectilinear motion, including those which lie inthe section plane (WO 95/31143) and those, in more widespread use, whichslope relative to said plane like the blade of a planing tool (e.g. U.S.Pat. No. 4,662,370).

The blade is driven in the same way, i.e. by means of a motor or turbinewhose rotary outlet shaft is connected to the blade either without anymodification to its motion, in which case the blade is rotary, or elsewith the continuous circular motion of the motor being transformed intoreciprocating linear motion by a peg secured to the shaft engaging in agroove secured to the blade which then oscillates in a directionperpendicular to the direction of its advance.

The means for moving the cutter blade through the cornea to be resectedhave in common a ring for fixing a, base of the apparatus on the eye,which ring carries guide means that co-operate with a blade-carrier headwithin which the motion of the blade is sustained. These guide means areof two types, either slideways (generally rectilinear slideways) inwhich the blade-carrier head is slidably mounted (see document U.S. Pat.No. 4,662,370), or else a pivot about which the blade-carrier head ispivotally mounted (see document U.S. Pat. No. 5,586,980).

The movement of the blade-carrier head along the fixed guide means isdriven by the hand of the surgeon. It is limited by an abutment whencutting of the cornea is to be limited to forming a flap that remainsconnected to the cornea. Proposals have recently been made to motorizethis movement by causing rotating means carried by the blade-carrierhead to co-operate with fixed means carried by the fixing ring so thatthe rotating means can roll without sliding along the fixed means (inthis context, see the following documents: U.S. Pat. Re 35,421, U.S.Pat. No. 5,624,456, U.S. Pat. No. 5,980,543).

Present devices with motorized advance are devices which the surgeonfinds complicated to use. It is not easy to adjust the beginning and theend of the cutting trajectory of the head, and there is no way to act onthe travel speed of the blade-carrier head since there is only one motorfor driving both the reciprocating motion of the blade and the gearingfor advancing the keratome relative to the ring with a speed reductionthat locks the frequency of oscillation of the blade and its speed ofadvance in a ratio that is defined by construction. Finally, thosekeratomes are not suitable for use by surgeons who prefer to applymanual control over the advance of the keratome across the ring.

OBJECTS AND SUMMARY OF THE INVENTION

The present invention seeks to remedy those drawbacks with amicrokeratome that is simple to use and that offers the advantage ofsatisfying all of the requirements that have been expressed by surgeons.

To this end, the invention thus provides a device for surgery of thecornea, comprising:

-   -   an annular base for fixing the apparatus to the eye of a        patient;    -   a cutter head comprising a body and a blade suitable for being        displaced along a plane trajectory parallel to the annular base;    -   guide means for guiding the cutter head relative to the base;    -   drive means for driving the blade in the cutter head with        reciprocating linear motion parallel to its cutting edge; and    -   drive means for driving the cutter head relative to the annular        base along said trajectory.

According to the invention, said drive means comprise two independentmotor units surmounting the cutter head and having mutually paralleloutlet shafts perpendicular to the plane of the trajectory of the cutterhead.

The independence of these drive means provides numerous advantages. Itis thus easy with simple electronic means for the operation of each ofsaid means to be servo-controlled to determine fixed or variableparameters and to conditions defining a relationship between them.

Thus, the surgeon can adjust the rate of advance of the cutter headalong its trajectory that makes it possible to adjust the rate ofadvance to the surgeon's own practices. The controlling electronics canprovide for the cutter head to advance at a rate that varies, e.g. as afunction of the variation in the surface area of cornea that is incontact with the blade. It is also possible to provide for oscillationto be interrupted during the return stroke of the cutter head.

It is also possible to provide safety features governing the drive whichadvances the head, specifically stopping the advance if oscillationstops or is faulty, making it impossible to start in the event of afailure of the suction system for holding down the annular base to theeye.

The two drives provided by the invention make it possible for thesurgeon to fix the starting point of the trajectory accurately andwithout possible error so that, at the starting point, the blade isalways out of contact with the cornea regardless of the diameter of thecorneal flap that it is desired to obtain.

Finally, it should be observed that the independence of the drive meansmakes it possible to eliminate all of the mechanical gearing, wheel, andwormscrew means that used to be necessary and received in the head fortaking transmission from the oscillation shaft for the purpose ofadvancing the cutter head. Unfortunately, such drive takeoff can only beperformed via metal parts since they are the only parts that make itpossible to achieve the manufacturing precision required for suchsmall-sized equipment constituting micromechanics. The drive takeoffthus used to provide electrical continuity between the microkeratomemotor and the fixing base or ring so the patient was not protectedagainst electrical failure of the equipment during an operation. Byeliminating this drive takeoff, the invention makes it possible to use ashaft of dielectric material (plastics material) at the outlet of themotor that drives advance of the head, thereby forming an insulatingbarrier between the electrical power supply of the motor and the fixingring (base) in contact with the patient's eye.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will appear onreading the following description of embodiments given below withoutlimiting character.

Reference is made to the accompanying drawings, in which:

FIG. 1 is a longitudinal section view of a microkeratome of theinvention;

FIG. 2 is an outside view of the end of the common case for the twomotors whereby said case is coupled to the cutter head;

FIG. 3 is an outside view of an embodiment of the body of the cutterhead suitable for fitting to the end of the case as shown in FIG. 2;

FIG. 3A is a side view of a cutter head of the kind shown in FIG. 3 andfitted with a cutter blade;

FIGS. 3B and 3C are fragmentary plan views of blades suitable for use ina microkeratome of the invention;

FIG. 4 is an outside view of a variant embodiment of the body shown inFIG. 3;

FIG. 5 is an outside view of part of the case and of the cutter headassembled together with a device for locking the assembly on the annularbase (not shown) for fixing the apparatus on the patient's eye;

FIG. 6 and FIG. 7 are two views of the underside of FIG. 5 showing theinactive and the active states of the locking device;

FIG. 8 is a simplified plan view of the device of the invention showingtwo extreme points of the trajectory of the cutter head relative to theannular base of the device;

FIG. 9 shows the cutter head coupled to its drive means, together with amember for adjusting the end point of the cutting stroke;

FIG. 10 is an outside view of the annular fixing base of the device,together with means for adjusting the end point of the stroke of thecutter head; and

FIG. 11 is a view from beneath and in perspective of the device of theinvention in which the annular base is a variant embodiment of thatshown in

FIG. 10, and the cutter head coupled to its drive means is as shown inFIG. 5.

MORE DETAILED DESCRIPTION

The device for surgery of the cornea as shown in the drawingsessentially comprises three portions. The first portion, given overallreference 100 in the figures, forms an annular base for fixing thedevice to the eye of a patient. The second portion, given overallreference 200 in the figures, constitutes a cutter head for using ablade 201 that it includes to cut off a disk of the cornea or to cut thecornea so as to leave a flap. The third portion 300 of the apparatus ofthe invention is constituted by drive means firstly for driving thecutter head 200 and secondly for driving the cutter blade 201 inside thecutter head.

The annular base 100, shown in particular in FIGS. 1, 8, 10, and 11comprises a ring 101 formed by a flat annulus 102 fitted with aperipheral skirt 103. In conventional manner, the inner periphery of theflat annulus 102 and the bottom edge of the skirt 103 come into airtightcontact with the eye of the patient and co-operate with the eye todefine an internal annular chamber which is connected to a source ofsuction via an orifice 104 and a tube disposed inside a handle 105.Thus, the cornea to be operated on projects into the inside of the ring101.

The ring possesses, integrally formed therewith, a pivot 106 whichextends perpendicularly to the plane of the flat annulus 102. The topend of the pivot 106 is provided with portions in relief implemented inthis case in the form of a mortise 107. In FIGS. 1, 10, and 11, this topend possesses, beneath the mortise 107, a groove 108. In FIG. 8, thepivot shown has at its top end a lateral surface with a first zone 109of diameter smaller than a second zone 110, the zone 110 being fittedwith a groove 111 whose bottom has the same diameter as the zone 109.

The pivot 106 is situated in a zone of the ring 101 that issubstantially diametrically opposite the handle 105. The handle 105 isconnected to the ring 101 via a bottom piece 112 which provides asubstantially radial abutment surface 113. In the case shown in FIG. 10,the handle 105 has a sliding piece 114 fitted with a set of spacers 115formed on a star-shaped piece whose branches are of differentthicknesses. The piece 114 is pressed against the piece 112 by means ofa spring 116. It will be understood that when the piece 114 is raisedagainst the spring 116 along the handle 105, the branches of thestar-piece 115 are disengaged from the abutment 113, thus making itpossible to select the branch of appropriate thickness for coming intoabutment against the surface 113. Each of the branches then offers asurface 115 a in front of the surface 113 and spaced apart therefrom bya distance equal to the thickness of the branch. It will be observedthat the piece 115 is mounted to rotate about a pin 117 carried by thepiece 114.

In the case shown in FIG. 11 and in FIG. 1, the handle 105 possesses anouter sleeve 118 fitted at its bottom end with a plurality, e.g. threeprotuberances 119, 120. This sleeve can be indexed angularly about thehandle 105 so that one of the protuberances 119, 120 presents anabutment surface 119 a or 120 a similar to the abutment surface 113 orthe abutment surface 115 a of FIG. 10. The protuberances 119 and 120 areof different circumferential sizes so that the abutment-forming surfaces119 a and 120 a are angularly closer to or further from the pivot 106depending on the size of the protuberance. The sleeve 118 can be indexedabout the handle 105 by means of a fluted portion 121 of the handlecovered by a correspondingly fluted portion of the sleeve 118, a nut 122in screw engagement on the handle 105 enabling the sleeve 118 to bepressed against the handle-receiving piece 112 while it is engaged withthe fluting 121, or when the nut is loosened, enabling the sleeve 118 tobe slid so as to change the protuberance that is in service. It wouldnot go beyond the ambit of the invention to provide a spring at the topof the sleeve 118 instead of and replacing the nut 122, like the springshown in FIG. 10.

The cutter head 200 visible in FIGS. 1, 3, 3A, 4, 5, 8, 9, and 11 is ofa general shape that is already described in the art. This cutter headpossesses a one-piece body 200 a having a top surface 203. It has abottom surface which is its surface that faces towards the fixing ring101 to slide thereon. In the example shown in the figures, it comprisesno more than a surface 220 and a surface 221, both lying in a commonplane. The body possesses firstly a through orifice 204 opening out intothe surfaces 220 and 203 and suitable for receiving the pivot 106. Thisbody also defines, perpendicularly to the axis of the orifice 204, ashelf 205 whose bottom face is spaced apart from the surfaces 220 and221 and whose function is to flatten the cornea immediately ahead of thecutter blade. The body 200 a also possesses, following the shelf, anorifice 206 for receiving and guiding the cutter blade 201 shown inFIGS. 1, 3A, 3B, and 3C. This cutter blade 201 possesses a blade-carrier201 a with a groove R formed in the top surface thereof perpendicularlyto the cutting edge 201 b of the blade, which cutting edge issubstantially parallel to the rear edge of the shelf 205, the groovebeing for receiving an eccentric finger on the outlet shaft of the bladedrive motor. The body 200 a opens out immediately behind the shelf 205so as to enable the blade to project and its cutting edge 201 b to besituated beneath the bottom face of the shelf 205 and behind its rearedge 205 a by a calibrated distance (d1, d2) which depends on thethickness of the corneal flap to be made. The body 200 a presents adeflector surface 207 above said opening and immediately behind theshelf 205, where such a surface 207 is likewise well known in the stateof the art and forms a sliding surface over which the corneal flapslides as cutting progresses.

An orifice 208 parallel to the orifice 204 opens out into the inside ofthe body 200 a from the top surface 203 of the body 200 a. In FIG. 3, itcan be seen that the orifice 208 is extended by means 209 of the femalebayonet coupling type which enable the head to be coupled to the end ofthe keratome drive means 300. In FIG. 4, the bayonet means arerepresented as being in the form of a sleeve 210 with studs thatpenetrate into and co-operate with female means provided in the drivemeans 300. The orifice 208 enables the blade drive finger to reach thegroove R in the blade support 201 a.

It will be observed that the body 200 a has a lateral projection 211 inthe vicinity of its top surface 203, which lateral projection 211 has asurface 211 a substantially parallel to the axis of the orifice 204,said surface 211 a forming abutment means for co-operating with one ofthe surfaces 113, 115 a, 119 a, or 120 a provided on the angular base ofthe device.

The orifice 206 for the blade 201 and its blade-carrier 201 a can eitherpass right through the body 200 a of the cutter head 200, or else can belimited by an end partition. The partition could be a web in continuitywith the side surface of the head shown in FIG. 3 adjacent to the bore204.

With a through orifice, as is provided mainly in a multiple-use headmade of metal, it is necessary to prevent the assembly comprising theblade 201 and the blade-carrier 201 a from escaping from its housingonce it has been inserted therein, before the head is mounted on themotor assembly 300, and while the surgeon is performing themanipulations necessary to achieve said mounting. For this purpose, theorifice 206 possesses a small cavity 206 a for receiving a stud 201 ccarried at the end of a resilient tongue 201 d which is integral withthe support 201 a of the blade 201 (see FIGS. 3A, 3B, and 4). While theblade is being inserted into the orifice 206, the tongue 201 d is curvedelastically until the stud 201 c rises and is received in the cavity 206a. The blade is then retained in the orifice 206. It can neverthelessoscillate in said orifice 206 under drive from the eccentric drivefinger since the length of the cavity 206 a measured in the oscillationdirection is greater than the amplitude of said oscillation. The bladeis also held in the housing in a position such that the groove R of theblade-carrier 201 a is held in a region of the head which is necessarilyscanned by the eccentric drive finger as soon as the motor begins torotate, and possibly as soon as the head is mounted on the drive block300. In this respect, it is advantageous for the groove R to flareupwards so that penetration of the drive finger is facilitated.

When the body 200 a is closed by an end web, as is the case mainly for asingle-use head 200 made of plastics material, it needs to be deliveredfitted with its blade. The stud 201 c then serves as a member forholding the blade in the single-use head 200 from manufacture until use.

In a variant embodiment of the blade 201, shown in FIG. 3C, the support201 a is provided with a projecting tip 201 e extending beyond the edgeof the blade 201 and which serves as a guide for inserting the blade inthe housing 206.

When the cutter head 200 is mounted to pivot about the pivot 106, itstrajectory is plane, perpendicular to the axis of the pivot 106, andthus parallel to the ring 101.

The drive means 300 comprise a case 301 containing two motor units 302and 303, whose bodies are prevented from rotating relative to the case,and which have respective outlet shafts 304 and 305. The outlet shaft304 of the motor unit 303 has an extension shaft 306 secured thereto andconstrained to rotate therewith, with the end 307 of the extension shaft306 being close to the end 301 a of the case. The end 307 of thisextension shaft 307 is in the form of a tenon of dimensions that adaptit for penetrating without clearance into the mortise 107 situated atthe top of the pivot 106.

In FIG. 2, it will be observed that the end 301 a of the case 301 is amachined part of relatively complex shape, having, in line with theshaft 306, a partially cylindrical recess 308 on the same axis as theshaft 306 but of smaller diameter, such that one of the edges 309 ofthis recess forms an angular abutment for the tenon 307. The tenon 307does not have the same length as the diameter of the shaft 306, but itis shorter so that one of its ends can rotate freely in the recess 308while its other end is constrained to come into abutment against theedge 309 thereof. It will be understood that this edge 309 thusconstitutes an abutment for angularly indexing the tenon 307 relative tothe case 301.

The outlet shaft 305 of the motor 302 is also extended by a shaft 310whose end has an eccentric finger 311 for driving the blade 201. Thisshaft 310 is surrounded at its end with a sleeve 312 (only the sleeve312 is shown in FIG. 2, the shaft 310 being omitted in order to clarifythe drawing), said sleeve 312 being constrained in rotation relative tothe end piece 301 a of the case 301, but being capable of a small amountof axial displacement along the shaft 310 against an annular rubberspring 313 which tends to cause it to retract somewhat into the endpiece 301 a. The sleeve 312 is provided with a collar 314 ofnon-circular shape that provides male bayonet coupling means forengaging the female bayonet coupling means 209 of the body 200 a of thecutter head 200, as shown in FIG. 3.

FIGS. 5, 6, and 7 show the elements 300 and 301 a fitted with a latchformed by a ring portion 315 mounted to rotate in a groove 316 of thepiece 301 a. This ring 315 has a downwardly extending arm 317 providedwith an inwardly directed tooth 318, said tooth extending at a levelthat is slightly offset from the tenon 307 towards the free end of thepiece 301 a. As can be seen in FIGS. 6 and 7, when the ring 315 is in aninactive state (FIG. 6), the tooth 318 is received in a recess 319 ofthe end piece 301 a. When it is in an in-service state (FIG. 7), thetooth 318 interferes with the recess 308 so that when the pivot isreceived in said recess it penetrates into the groove 108 of the pivotand prevents any axial separation between the annular base 100 and thepiece 301 a, which naturally carries the cutter head 200.

In order to perform an operation, the surgeon begins by assembling thecutter head 200 already fitted with its cutter blade 201 to the drivemeans 300. To do this, the means 209 of the head 200 are engaged withthe means 314 at the end 301 a of the assembly 300. The fixed angularorientation of the means 314 is such that this engagement can beachieved only if the head is offset angularly relative to the piece 301a, i.e. if the axes of the housing 204 and of the shaft 306 do notcoincide. Once axial engagement has been achieved, the surgeon pivotsthe head 200 about the axis of the shaft 310 received inside the means314 so that they co-operate like a bayonet coupling with the means 209,thus preventing any axial separation of the head 200 from the case 301.This rotation is done so as to move the axis of the orifice 204 towardsthe axis of the shaft 306. These axes are brought into alignment when,for example, an abutment 320 (a peg) comes to bear against a surface 212of the body 201 of the cutter head (see FIG. 5). Advantageously,provision is also made for the head to be indexed on the case, e.g. bymeans of a flute 213 (FIG. 3) formed in the top surface 203 of the headwhich receives a ball 31 (FIG. 6 and FIG. 7) projecting under drive froma return spring from the end face of the piece 301.

It will be understood that the head 200 of FIG. 4 is mounted on the bodyof the case 301 in the same manner except that the male and femalebayonet coupling means are interchanged compared with the above example.In this respect, it will be observed that the means 210 which performthis bayonet coupling are not symmetrical, thus constituting keyingmeans to ensure that the head cannot be wrongly mounted to the motorassembly case. Such asymmetrical coupling means can also be used in thepreceding embodiment.

Once the elements 200 and 300 have been assembled together in this wayand prevented from moving axially and angularly relative to each other,the orifice 204 of the head 200 is in alignment with the shaft 306. Itwill be observed that the shaft 306 possesses control means such thatafter an operation has been performed it is returned to a fixed angularposition which is the position shown in FIG. 2, i.e. the tenon 307 bearsagainst the surface 309 of the piece 301 a. The surgeon places theannular base 100 on the patient's eye and holds it there by suction asdescribed above. Thereafter, the assembled-together elements 200 and 300are presented thereto so as to insert the pivot 106 in the orifice 204.To ensure that the tenon 307 penetrates into the mortise 107, thesurgeon must cause the set of elements 200 & 300 to pivot about thepivot 106, thereby defining one and only one relative angular positionbetween the base 100 and the assembled elements 200 & 300. This positionis the starting position for the operation. It is reached when thecutter blade is spaced apart from the cornea that is to be operated onspecifically because the tip of the tenon 307 rests against the tip ofthe pivot 106 until the tenon penetrates into the mortise. This providesadditional safety preventing any unwanted injury to the cornea by thecutter blade. When the tenon 307 has penetrated into the mortise 107 theassembled motor 300 and cutter head 200 rest against the annular base100 via the two coplanar surfaces 220 (surrounding the orifice 204) and221 (at the end of the lateral wall 222 of the body 200 a of the cutterhead 200 see FIGS. 3 and 3A). It will be understood that by varying thevertical distance D (FIG. 3A) between the bottom face of the shelf 205and said surfaces 220, 221 it is possible to vary the extent to whichthe portion of the cornea projecting into the center of the annular base100 is compressed by the shelf 205. Thus, the smaller this distance thegreater the extent to which the cornea is flattened; this means that acorneal cap of larger diameter is obtained than with a larger value forD. Thus, other things remaining equal, by providing a set of cutterheads 200 each having a different value for the distance D, the surgeoncan be given the possibility of choosing the diameter of the corneal capthat is to be obtained, so as to adapt said diameter in the bestpossible manner to the needs of the patient.

The trajectory followed by the cutter blade is thus circular, beingcentered on the axis of the pivot 106 and lying in a plane perpendicularto the axis of said pivot. By construction, the axes of the motors 302and 303 are then parallel to the axis of the pivot 106 and thusperpendicular to the trajectory followed by the cutter blade. It will beobserved that this ensures there is practically no overhang of themoving assembly relative to the fixed annular base throughout the entireprocedure for cutting the cornea. The weight of the motor 303 actspractically along the axis of the pivot, and the weight of the motor 302acts along an axis which never projects beyond the peripheral skirt 103of the annular base. The resultant of these two gravity forces thereforealways lies inside the annular base.

To implement an axial security link between the annular base and themoving assembly 200, 300, the invention provides various devices.

Firstly, there is the latch shown in FIGS. 5, 6, 7, and 11. When it isin the state shown in FIGS. 6 and 11, the latch does not interfere withthe pivot head which has passed through the orifice 204 and which isengaged with the tenon 307. By turning the ring 315 so as to bring thelatch into its active state, the tooth 318 is caused to pass under thepivot head 106 so as to be received in the groove 108 of the pivot. Itis then impossible to separate the moving assembly 200, 300 from thering 100, or for this moving assembly to be accidentally lifted duringan operation. The figures do not show the indexing and abutment deviceswhich are provided between the ring 315 and the piece 301 a to enablethe surgeon to feel the two positions of the latch and to ensure thatthe latch is not forced in a direction that would be harmful to themechanical quality of the equipment. These devices can merely beresilient snap-fastening systems and pegs that come into abutmentagainst suitable surfaces.

This locking function can be performed differently, as showndiagrammatically in FIG. 8. In this figure, continuous lines show thehead 200 at the end of its working stroke, and chain-dotted lines showthe head 200′ at the moment when the tenon 307 penetrates into themortise 107. The body of the head 200 a carries a stud 214 whichprojects into the orifice 204 in a well-determined angular position.When the tenon 307 penetrates into the mortise 107, the stud 214 issituated facing the lateral zone 109 of the pivot 106 which is ofdiameter smaller than the inside diameter of the orifice 204, thusenabling the projecting portion of the stud 214 to avoid interferingwith axial sliding of the head over the pivot 106. This stud is then inits position 214′, i.e. immediately at the entrance to the groove 111which carries the zone 110 of the pivot which is itself of a diametersubstantially equal to the inside diameter of the orifice 204. It willbe understood that as soon as pivoting of the head 200 about the pivot106 is initiated in order to move it from its position 200′ to itscontinuous line position in FIG. 8, the stud 214 engages in the groove111. Throughout the duration of cutting and return of the moving portionabout the pivot 106, no axial separation is possible between the movingportion 200 & 300 and the fixed annular base. With a microkeratome thatis suitable for being fitted with a selection of heads that differ fromone another as to the value D shown in FIG. 3A, then the inventionprovides axial security link means that accommodate these differentsizes in simple manner.

In a first variant (not shown), the annular base 100 possesses aremovable pivot 106 (e.g. because it is secured to the ring by screwengagement), thus enabling the pivot to be matched with the head used.For a head with a small value of D, the tenon 307 and the tooth 318 ofthe ring 315 are closer to the top surface of the ring 101. Thecorresponding pivot for fitting to the ring should therefore be shorterthan for a head with a larger value of D so that the tenon 307 does notcome into abutment against the bottom of the mortise 107 and the groove108 is not too high relative to the tooth 318.

In another variant, a single base 100 can be provided for all of theheads by making a mortise 107 that is sufficiently deep to receive atenon 307 that is sufficiently long to accommodate all differences inheight between the cutter heads because of the different dimensions D.To adjust the link mechanism, an arm 317 is then provided that is of alength which is adjustable by means of two telescopic portions and anindexing system for causing the length of the arm to correspond to theselected head.

In a third variant, the keratome of the invention has a set of heads 200with each having a distance D that is determined as a function of thediameter of the corneal cap to be obtained, and a complete set ofangular bases each corresponding to one of the heads. These dispositionsare advantageous, particularly when single-use cutter heads and basesare provided that are made out of synthetic material.

As described above, the starting point of the trajectory followed by thecutter head is determined by the angular orientation of tenons in thepiece 301 a. The surgeon can then switch on the motor 302 which givesrise to high frequency reciprocating motion of the blade 201. Thesurgeon then switches on the motor 303. Since the shaft 306 associatedwith this motor cannot turn because of the tenon-mortise connectionbetween said shaft 306 and the fixed pivot 106, it is the body of themotor that turns about the shaft 306, and thus the entire case 301 andthe cutter head 200 which is associated therewith. This moving assemblystops turning when the lateral projection 211 secured to the cutter head200 comes into abutment against one of the surfaces 113, 115 a, 119 a,or 120 a depending on the embodiment shown, which surfaces are allcarried by a piece that is secured to the annular base 100. By means ofa suitable detector, e.g. responsive to an increase in the power supplycurrent drawn by the motor 303, the power supply to the motor isswitched off or reversed so as to cause the head to return to itsinitial position. It is recalled that this initial position is obtainedby the tenon 307 coming into abutment against a surface 309 carried bythe piece 301 a. In this case, likewise by means of an appropriatesensor, the sudden increase in torque opposing rotation is detected andthe power supply to the motor 303 is switched off. The portions 200 and300 can then be removed from the annular base 101 and any desiredintra-stroma ablation can be performed while keeping the corneal capraised, in particular by using a procedure known under the name LASIK.

It will be understood that the final position of the cutter headdetermines the position, the length, and thus the mechanical qualitiesof the “hinge” link zone between the flap that has just been cut freeand the eye. The surgeon must be capable of acting in this finalposition. It must thus be possible to move the abutment surface 113 thatis secured to the annular base 100. For this purpose, the inventionproposes a variety of embodiments to achieve this result, as shownrespectively in FIGS. 10, 11, and 9.

By using the device described above with reference to FIG. 10, thesurgeon can replace the abutment surface 113 with a selected one of fouravailable surfaces 115 a thus enabling the position of the end point ofthe trajectory of the cutter head to be adjusted.

In FIG. 11, it is the surfaces 119 a and 120 a that can be putselectively into operation by rotating the sleeve 118 carrying them soas to achieve the same result.

Finally, FIG. 9 proposes a third variant embodiment in which action isno longer taken on the surface 113 secured to the annular base 100 buton the surface 211 a secured to the projection 211 carried by the body200 a of the cutter head. When the head 200 is assembled to the case301, the case has an outside surface suitable for receiving a kind ofclip 215 which possesses a spacer 216 capable of bearing against thesurface 211 a of the projection 211 and thus of presenting an abutmentsurface 216 a that co-operates with the surface 113 of the piece 112 ofthe base 100. The surgeon has a set of clips 215 so as to have spacers216 of a sufficient variety of different thicknesses to be able toobtain the desired adjustment.

The above description relates to an embodiment of the main means of theinvention applied to a pivoting keratome. It would not go beyond theambit of the spirit of the invention to provide two motors for akeratome having linear motion or even pivoting motion obtained byco-operation between gears provided outside the head 200 and fixed racksprovided on the annular base. Although the motor for driving the bladein its reciprocating motion inside the cutter head remains substantiallyidentical in all variant embodiments, the motor 303 can have its outletshaft 306 engage a transmission, e.g. using gear wheels, with the lastgear wheel meshing with a fixed rack that can be rectilinear or curved.

It will be observed that having independent motors provides numerousadvantages to the surgeon as to flexibility in use of the microkeratome.In addition to those mentioned above, it can also be mentioned that thesurgeon finds it reassuring to be able to start the oscillating motionof the blade before starting the cutting movement of the cutter head,and it can be advantageous to continue the oscillating motion of theblade even after the movement of the cutter head has stopped.

Another advantage of two motors lies in enabling two types ofmicrokeratome to be manufactured on a standardized basis, one typehaving motor-driven advance and the other manual advance. For a manualadvance keratome, the only modification that needs to be made to thekeratome described above is minor and lies in omitting the mortise 107at the end of the pivot 106. Under such circumstances, the surgeon canactuate the assembled elements 200 and 300 manually about the pivot 106after locking them to the pivot. Nevertheless, this loses the advantageof having a starting position that is determined and fixed. To retainthis advantage, a simple modification to the keratome of the inventionconsists in omitting the motor 303 and in replacing it with a piece thathas an end tenon like the shaft 306. This piece is subject to arelatively small amount of return torque about its longitudinal axisthus pressing the tenon against the surface 309 of the piece 301 a asdescribed above. Under such circumstances, the three portions of thekeratome are assembled together and mounted in the same manner as thatdescribed above, with the manual advance movement of the cutter headover the ring of the annular base being performed manually against themember which exerts the above-mentioned return torque on the tenon.Finally, this manual version is easy to motorize. All that is needed isto perform the opposite substitution to that described above, i.e. thepeg having a tenon with return torque applied thereto is replaced by amotor unit such as the unit 303 as described above.

1. A single use cutter head assembly to be used with a microkeratome forslicing a sliver of corneal tissue comprising: a body with mountingfeatures for coupling said body to drive means of said microkeratome; anorifice made in said body; a blade assembly located in said orifice tobe housed and guided therein; and said blade assembly comprising a bladeand a blade carrier connected to said blade, said blade carrier having aresilient tongue with a stud, and wherein said orifice includes a cavityin which said stud is located.
 2. A single use cutter head assemblyaccording to claim 1, wherein said orifice extends completely throughsaid body.
 3. A single use cutter head assembly according to claim 1,wherein said orifice is limited by an end partition in continuity with aside surface of said body.
 4. A single use cutter head assemblyaccording to claim 1, wherein said body is a one-piece body formedintegrally from one piece of material.
 5. A single use cutter headassembly according to claim 1, wherein said stud is able to freely moveback and forth within said cavity, as said blade assembly is guided backand forth inside said orifice.
 6. A single use cutter head assemblyaccording to claim 1, wherein said cavity has a length measured in adirection of oscillating movement of said blade assembly greater than anamplitude of said oscillating movement of said blade assembly.
 7. Asingle use cutter head assembly according to claim 1, wherein saidresilient tongue extends away from a side edge of said blade carrier,and said stud is located at an end of said resilient tongue remote fromsaid blade carrier.